1. Field of the Invention
The present invention relates to a semiconductor apparatus such as an IC (integrated circuit) package and its manufacturing method.
2. Description of the Prior Art
Generally, semiconductor apparatuses such as IC packages are manufactured through processes such as a die bonding process (chip bonding process), a wire bonding process and a resin molding process. These processes are executed with respect to lead frames.
FIG. 1 is a plan view showing a principal portion of an example of a lead frame for use in a conventional QFP (quad flat package). P shows an area corresponding to one package. A lead frame 21 includes an island 22 on which a semiconductor chip is to be provided, a plurality of inner leads 24 connected to electrodes of the semiconductor chip provided on the island 22, outer leads 25 formed continuously from the inner leads 24 and used for connection to a substrate, and a guide rail 26 provided with a guide hole 26a for positioning.
Moreover, the lead frame 21, which is manufactured for every semiconductor device according to specifications such as a configuration and the number of terminals of a semiconductor chip bonded onto the island 22, is generally formed by punching a thin conductive metal plate by use of a punching metal mold or by using an etching method in which the thin conductive metal plate is brought into contact with etchant through a mask having a predetermined opening pattern.
To manufacture a semiconductor apparatus by use of the lead frame 21, first, a semiconductor chip is bonded onto the island 22 of the lead frame 21 in the chip bonding process. Then, the tips of the inner leads 24 extending toward the island 22 and electrodes of the semiconductor chip are connected with gold wire in the wire bonding process. Thereafter, the island 22 and the inner leads 24 are molded by being encapsulated in resin in the resin molding process, and the molded portion is cut off from the lead frame 21 in a lead cutting process. The molded portion which is cut off is a completed semiconductor apparatus.
The thickness of a semiconductor apparatus such as an IC package depends on the sum of the thickness of the lead frame 21, a semiconductor chip provided on the island 22 and wire for bonding.
Since the lead frame 21 is manufactured by punching a flat metal plate of uniform thickness or by etching as described above, the island 22, the inner lead 24 and the outer lead 25 are formed to be of the same thickness. Generally, the thickness is 0.25 mm in DIPs (dual in-line packages), and 0.15 mm in SOPs (small outline packages) and QFPs.
Therefore, in order to realize a thinner semiconductor apparatus, the lead frame 21 must be thinner. If the entire lead frame 21 is thinner, however, the outer lead 25 required to have mechanical strength may not sufficiently be strong, or the heat conduction capacity thereof may decrease.
In order to solve such a problem, it is considered to increase the thickness of the lead frame 21 until the outer lead 25 is sufficiently strong. In this case, however, manufacturing of semiconductor apparatuses having a large number of terminals which manufacturing requires fine processing is impossible. That is, in order to increase the number of terminals of a semiconductor apparatus without changing its dimensions, pitch fining of the inner lead 24 must be realized. Since whether the pitch fining is possible or not depends on the thickness of a metal plate of which the lead frame 21 is made, the pitch fining of the inner lead 24 is limited if the lead frame 21 is thick. As a result, it is impossible to realize a thinner semiconductor apparatus which requires to have a finer pattern.
To solve these problems, it is considered to form a lead frame 21 where the island 22 and the inner lead 24 are formed to be thinner than the outer lead 25. However, merely thinning the island 22 introduces another problem that the island 22 is distorted in providing a semiconductor chip onto the island 22 in the die bonding process. Moreover, if a portion where the island 22 and the inner lead 24 are formed is made thinner than the outer lead 25 by pressurizing it through rolling or stamping, since the portion to be formed thin is surrounded by a non-processed portion such as the outer lead 25 as shown in FIG. 1, the entire lead frame 21 is distorted.